1. Field of the Invention
This invention relates to sliding vane positive displacement pumps, and more particularly to such a pump having a spring biased mechanical vane actuating system.
2. Description of the Prior Art
One of the primary concerns in using positive displacement pumps of the sliding vane type is maintaining the vanes in contact with the inner surface of a liner along which the vanes ideally move in transporting liquids through the pump. As is known to those skilled in the art, there is natural centrifugal force acting outwardly on the vanes as the rotor rotates. However, in many applications, and particularly with fluids of high specific gravity or high viscosity, the vanes will lift from the inner surface, and thus fluid will slip by the vanes. The result is a decrease in pumping efficiency. Many means have been devised to place additional outwardly acting forces on the vanes in addition to the centrifugal force so that the vanes will track the inner surface properly for maintaining higher efficiency.
In one method, holes are drilled through the rotor interconnecting opposite pairs of vanes. A solid pin is slidingly positioned in the hole such that as one vane moves inwardly, the opposite vane is forced outwardly. A problem with such a system is that the dimension across the liner may not be constant. If this is the case, the pin must be somewhat shorter than the normal distance between the two innermost edges of the opposite vanes. Even if the distance across the liner is constant, the solid pin arrangement allows no compensation for wear on the outer edges of the vanes. In either case, the result is that the pin has some movement between the vanes and is not maintained in constant contact with the inner edges thereof. The pin is thus bounced back and forth between the vanes as the rotor turns. In other words, the pin impacts the inner surface of each of the opposite vanes for each revolution of the rotor. At the high speeds with which positive displacement pumps may be operated, the force of impact of the pin on the vanes can be quite high, quickly resulting in damage to the vanes. One solution has been the use of hard metal bumpers attached to the vanes to protect the inner surface. The result is an expensive vane, and the pins will eventually wear the bumpers as well.
Another method of providing outward force on vanes for sliding vane pumps is the use of a coil spring positioned between the inner surface of the vane and the rotor slot. One such arrangement is shown in U.S. Pat. No. 2,541,405 to Chapman, in which a hole is countersunk in each vane to contain and guide the spring. In the fluid motor of Adams, U.S. Pat. No. 2,899,941, both the rotor and the vanes have countersunk holes. There are many variations on the spring actuated vane arrangement. This system has the advantage of compensating for wear on the outer surface of the vanes, but a frequent problem is wear on the outer surfaces of the spring. Also, countersinking holes in the vanes results in a weakness which is frequently unacceptable in modern pumps which utilize plastic materials for the vanes. Because the springs are not totally contained, there is the possiblity that they may be skewed slightly which could have a detrimental effect on blade actuation.
Another solution has been the use of two pins disposed in a hole intercommunicating two opposite slots with a spring positioned therebetween. This arrangement contains the spring sufficiently so that it will not skew, but still has the disadvantage of wear on the outer surfaces of the spring because the spring must slide in the hole in the rotor along with the pins. Another disadvantage of the multiple pin and spring arrangement is that the pins and springs must be installed separately.
The vane actuating system of the present invention has the advantages of spring actuation to help compensate for vane wear, and also has the advantage over the prior art of totally containing the spring such that the spring does not slide back and forth in the hole in the rotor. Thus, the wear life on the spring is greatly increased. Also, in the vane actuating system of the present invention, a retainer pin is used so that the assembly can be installed in the pump as one piece, so there are no loose parts.